OpticalLimits, formerly known as photozone.de has completed their testing of the Canon 70-200 F4L IS II.
Their conclusion? I think they like it .. and give it their highly recommended seal of approval.
From their conclusions;
The king is dead and, yes, long live the new king. The Canon EF 70-200mm f/4 USM L IS II is everything that the mk I was plus some. It is the perfect playmate for ultra-resolution Canon cameras. It is mostly tack sharp at mainstream settings with no real weakness across the focal length range. Lateral CAs are low and not really an issue. Image distortions can be visible specifically at the long end though and you can spot some moderate vignetting at f/4. If you use digital auto-correction that will be a lesser concern, of course. The quality of the bokeh is Okay for a zoom lens but it has its shortcomings.
Also if you are interested in seeing more Canon 70-200 F4L IS II goodness, check out the dpreview sample gallery just posted here.